In general, color output devices such as televisions, color monitors and color printers are capable of displaying a variety of colors by combining only a few colors. For example, televisions and color monitors typically combine the colors red, green and blue to produce a spectrum of colors. Similarly, color printers typically use cyan, magenta and yellow to produce a spectrum of colors. Color printers often further use the color black.
Computer systems which include color output devices (e.g., a monitor, a printer, etc.) typically provide colors based on digital color representations in a color system or color space. For example, a typical color monitor provides colors according to color representations in RGB color space. RGB stands for red, green and blue. In a similar manner, a typical color printer provides colors according to color representations in CMY color space. CMY stands for cyan, magenta and yellow.
A typical color representation is a series of computer readable bits which identify a combination of colors within a color space. Accordingly, a color representation in RGB color space indicates amounts of red, green and blue which combine to form a particular color. Similarly, a color representation in CMY color space indicates amounts of cyan, magenta and yellow which combine to form a particular color.
Some computer color management systems can convert color representations in one color space into corresponding color representations in another color space. For example, some color management systems can convert a particular color representation in RGB color space into a corresponding color representation of that same color in CMY color space.
An organization called CIE, the Commission Internationale de l'Eclairage, has developed other color systems. One such color system is called the CIEXYZ color system. The CIEXYZ color system refers to a device independent color space which is based on three theoretical colors X, Y and Z. The CIE selected these colors such that all colors which are perceivable by the eye of “a standard observer” lie within the CIEXYZ color space.
Another CIE color system is the CIELAB color system. This system refers to another device independent color space which is based on the same theoretical colors X, Y and Z but defines color space coordinates in terms of brightness (L), a relative green-red sensation (a), and a relative blue-yellow sensation (b). Hue (h) and chroma (c) are derivable from these coordinates. In particular,h=arctan (b/a), and c=(a2+b2)(1/2).A thorough description of the CIEXYZ and CIELAB color systems is provided by Publication CIE 15.2-1986, the entire teachings of which are hereby incorporated by reference in their entirety.